Anyone figure how to use the RCA AUX input?

Here's one from eBay I may just try out myself:
http://www.ebay.com/itm/3-5mm-aux-Line-out-to-30P-female-Cable-for-apple-iPhone-3G-4G-4S-iPod-Touch-Nano-/231029710951?pt=US_MP3_Player_Cables_Adapters&hash=item35ca71a067



